1. Field of the Invention
The present invention relates to a rotor of a brushless motor.
2. Description of the Related Art
In the conventional practice, motors are used as driving sources of various types of apparatuses and products. For example, the motors are used for business machines, such as printers and copying machines, various kinds of home electric appliances, and power assist sources of vehicles, such as automobiles and power-assisted bicycles. In particular, brushless motors are sometimes used as the driving sources of movable parts with high operation frequency in the light of increased durability and reduced noise.
Known as a type of such a brushless motor is an interior permanent magnet (IPM) motor where a permanent magnet is embedded in a rotor. For example, electric appliances are known in which a plurality of plate-like magnets are radially embedded in a rotor yoke and the magnets are disposed such that the same poles of adjacent magnets face each other in a circumferential direction of the yoke (see, for example, FIG. 2 of patent document 1).
[patent document 1] Japanese Translation of PCT International Application Publication No. JP2012-517209
One of the methods to improve a rotational torque of a brushless interior permanent magnet motor is to use a magnet with high residual magnet flux density. If the short circuit flux occurs inside a rotor, the average magnetic flux density is lowered at the outer circumference of the rotor yoke. This is addressed in the aforementioned electric appliances by forming near the magnet a through hole called a flux barrier with high magnetic resistance for preventing the short circuit flux at the ends of the magnet.
The fan-shaped rotor magnetic pole pieces in the aforementioned electric appliance are connected to the annular part around the central axis and are merely supported by a narrow area located between adjacent flux barriers. For this reason, the rotor magnetic pole pieces are displaced (vibrated) relative to the normal position due to various forces (centrifugal force and magnetic force) exerted on the rotor magnetic pieces as the rotor is rotated so that troubles such as rotational noise or rotor damages might occur.